A magnetic device, which uses a giant magnetic resistive (GMR) effect and a tunneling magnetoresistive (TMR) effect, includes a magnetoresistive element formed from an artificial grading multilayer film having about six to fifteen layers. The magnetoresistive element includes a fixing layer, which fixes the direction of spontaneous magnetization, a free layer, which rotates in the spontaneous magnetization direction, and a nonmagnetic layer, which is arranged between the fixing layer and the free layer.
The output characteristics of a magnetic device are greatly dependent on the electric resistance value of the magnetoresistive element. The electric resistance varies greatly in accordance with the thickness of each of the nonmagnetic layer, free layer, fixing layer, and the like. For example, when using an MgO layer as the nonmagnetic layer, even a slight change of 0.1 nm in the thickness of the MgO layer would vary the resistance value by 50% or greater (non-patent document 1). Thus, in a magnetic device using a GMR element or a TMR element, the thickness of each layer must be highly accurate to stabilize the output characteristics of the magnetic device.
A sputtering apparatus is widely used as a film formation apparatus for each layer of the artificial lattice multilayer film. The sputtering apparatus sputters a sputtering target (hereinafter, simply referred to as the target) and deposits sputter grains dispersed from the target onto a substrate. To improve the thickness uniformity of a thin film, there are sputtering apparatuses that incline a target surface relative to a substrate surface, turn the target around the substrate, or swing the target relative to the substrate (for example, patent document 1 and patent document 2). In such cases, the sputter grains dispersed from the target strikes the substrate from different angles. Thus, the sputter grains may be further uniformly deposited throughout the entire substrate surface.
When performing sputtering, the thickness uniformity of a thin film varies greatly in accordance with the discharge state or plasma density of a plasma discharge area above a substrate. The discharge state or plasma density above the substrate varies in accordance with the position of each point on the target surface relative to the substrate. For example, the trajectory of a sputter grain relative to the substrate and the density of the sputter grains vary in accordance with the coupling angle of the target in a circumferential direction.
During a single film formation process, the turning or swinging of the target is performed by combining a coupling angle having a high thickness uniformity and a coupling angle having a low thickness uniformity so that the film thickness between substrates becomes uniform. Thus, during a single film formation process, a thin film having low thickness uniformity may be formed. This makes it difficult to sufficiently improve the thickness uniformity of the thin film.    Non-Patent Document 1: Nature Mater. 3 (2004)868    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-339547    Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-111927